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An infinitely long uniform solid wire of radius $a$ carries a uniform dc current of density $\overrightarrow{j}$.

The magnetic field at a distance $r$ from the center of the wire is proportional to

1. $r$ for $r\lt a$ and $\frac{1}{r^2}$ for $r\gt a$
2. $0$ for $r\lt a$ and $\frac{1}{r}$ for $r\gt a$
3. $r$ for $r\lt a$ and $\frac{1}{r}$ for $r\gt a$
4. $0$ for $r\lt a$ and $\frac{1}{r^2}$ for $r\gt a$